Operation and Maintenance (O & M) of Ash Handling System in Thermal Power Plants

Are you looking for comprehensive information about the Ash handling system in Thermal power plants including its Operation and Maintenance (O & M)? If indeed, you are at the right place and do read this article till the end.

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Introduction: Ash Handling System in Thermal Power Plants

One of the most profound and earliest methods of generating electrical power from available resources is the conversion of thermal energy released by the burning of an organic fuel in a thermal power plant.

It is still a dilemma as energy production through thermal power plants leaves many waste elements, which can create harmful effects if not handled properly. In spite of this, thermal power stations are contributing a significant part in fulfilling the energy requirement of this world.

According to a paper published in 2017, typically for a 2×500 MW plant based on Indian coal, the ash generated is around 300 to 400 TPH, although the figure depends upon the gross calorific value as well as the content of the ash.

An Ash handling system in thermal power plants is an advanced technological method to control and manage the production of ash – one of the waste elements in every thermal power station. The hot residual ash is cooled down to a specific controlled temperature and stored properly through compliant systems.

Rather than disposing of this ash as a waste, an ash handling system helps recycle, store, and use it in different industries, including cement plants, construction sites, and allied industries. Hence, proper O & M of an ash handling system is of significant importance in any thermal power plant to improve its efficiency and production.

Operations in an Ash Handling System of Thermal Power Plants

An ash handling system involves the following critical operations. Mishandling in any phase can critically harm the operation of the whole system.

1. Removal of Ash from Furnace

When the fuel, let’s say coal, is burnt in the furnace of any thermal power plant, it produces a large amount of ash that needs to be removed. For many evident and technical reasons, it is incredibly harmful to keep that hot residual of ash in the furnace.  Some of them are given below:

1. Residual ash covers a significant volume of the furnace, which will impact the intake of fuel.
2. Hot ash can cause wear to the inside structure of the furnace due to its corrosive nature.
3. The efficiency of the furnace and the burning of fuel are affected.

2. Quenching Process

To prevent such consequences, ash is removed from the furnace and is quenched (passed through or dipped in water) in a separate container. The quenching process is done for the following reasons:

1. Reduce the temperature of ash up to a manageable degree
2. Lessen the corrosiveness of the residual ash
3. Prevent ash particles from scattering
4. Avoid the formation of clinkers

3. Transportation of Ash

After the quenching process is finished, the ash is then transported to another storage. This transportation can be carried out by four different means, depending on the plant’s requirements. Either of the following systems can drive the conveyors used to transport the ash in an ash handling system of a power plant:

1. Mechanical System
2. Pneumatic System
3. Hydraulic System
4. Steam-injector System

4. Collection in Ash Bunkers

Using any of the above-mentioned means of conveyor transportation systems, the ash is stored in ash bunkers. The ash can be used for various purposes (in the manufacturing of cement or construction sites) or disposed of in ponds when it settles down in the base.

NOTE: Some dust particles from ash enters the piping system, implanted to remove the residual gases. These particles are separated out in a dust collector. This dust collector prevents those corrosive and harmful particles from releasing into the environment and collecting them in a separate space.

Types of Ash Handling Systems and their Operations

Depending upon the nature of collecting and processing ash, the ash handling systems are mainly of two types.

1. Fly Ash Handling System
2. Bottom Ash Handling System

1. Fly Ash Handling System

The operations in a fly ash handling system consist of an ESP (electrostatic precipitator) ash system, an economizer ash system, and an air-preheater ash system.

The compressed air from compressors is transferred through pipes to the ash systems. A valve inside the pump allows the ash, collected in the hopper, to enter. The ash is then carried away through the pipers with the help of compressed air. This electrostatic precipitated ash is then transferred to the ash silo. Similarly, the economizer ash and the air-preheater ash is sent to the ash silo by the help of compressed air.

• Economizer ash particles have no typical size. The temperature of this ash ranges from 600°F to 900°F.
• In the air preheater system, the particle sizes range from 100 to 800 microns, while the ash temperature ranges from 250°F to 400°F.
• In the case of the Electrostatic precipitator ash handling system, the size of the fly ash particles entering the ESP can range from 0.01 micron to 1000 microns.

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2. Bottom Ash Handling System

The operations involved in a bottom ash handling system include the collection, cooling, and crushing of the furnished bottom ash. After these operations, the ash is collected into a bottom ash bunker. The ash that drops from the hot boiler is conveyed to a crusher using a conveyor belt sunk into the water at 60 degrees. The crusher breaks down the clinkers and turns them into fine particles, which are stored in the bottom ash bunker. For the bottom ash handling system, an ash hopper’s optimum storage capacity is in the range of 10 to 12 boiler hours’ output.

The ash from both, ash silo and bottom ash bunker, is then carried away by trucks or railways to their destined location to different plants.

Maintenance in an Ash Handling System of Thermal Power Plants

For any power plant to operate normally, proper handling and maintenance play a vital role. It is critical to check if all the equipment is following the same and the standard operating cycles. Failure in a single piece of equipment can lead to the system’s collapse, which may cause significant damage.

Here are some points that we carefully deem regarding an ash handling system of a thermal power plant.

1. Checking the wear in Bottom Ash Hopper

1. Falling of clinker ash pieces in the hopper can damage the lining.
2. There are chances of wear inside the flushing nozzles in the ash hopper.
3. Incorrect alignment of nozzles can cause an erosional effect.
4. Ash accumulation can distort the seal plate.

2. Maintenance of Clinker Grinder

1. A high concentration of ash in the slurry can cause a clinker grinder to stall.
2. The grinder would stop working if excessively packed material, pieces of slag, or erection debris entered.

3. Replacing worn parts of Jet pumps

Jet pumps require a sure concentration of ash to work at an optimum level. In case any jet pump wears from any part (body, tube, or nozzle), it is needed to be replaced urgently.

4. Prevention from Corrosion

It is necessary to use corrosion-resistant parts for hopper, discharge gate, jet, and grinder. The hopper water with a pH of 5.5 and corrosion can produce failure in the systems.

5. Taking Care of Pipelines in a pneumatic ash handling system

Preventive measures should be taken for the following causes:

1. Incorrect Air Mover Specification
2. Over Feeding of Pipeline
3. Moisture in Line
4. Pipeline Wear
5. Wear of Straight Pipeline
6. Leakage

Conclusion

Operations and maintenance (O & M) of an ash handling system in any thermal power plant is one of the crucial aspects. Whether it’s the proper functioning of a thermal power plant, achieving optimum efficiency, or making a process environment friendly, normal operations and timely maintenance of an ash handling system are critically important.

Depending upon the type of plant and its specific requirements, O & M of an ash handling system varies, but properly operated and well-maintained equipment ensures higher internal plant efficiency and optimized costs, notwithstanding higher project returns for the thermal power plant.

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